The present invention pertains to microelectromechanical systems. More particularly, the present invention pertains to double pinned micromechanical sensors.
In many industries there is a need for large quantities of low cost and reliable sensing devices. As a specific example, the automotive industry requires a high volume of accelerometers used in ride control, inertial navigation, and crash sensing for airbag deployment. In each of these applications as well as many others, reliability, and low costs are key requirements. While large scale mechanical devices have long been known, they are not capable of meeting all these requirements. Thus, micromechanical sensors, such as pressure sensors and accelerometers are being actively pursued.
In attempts to provide micromechanical sensors which will meet the desired requirements, designers have employed approaches based on piezoresistive, capacitive, and piezoelectric sensing, as well as resonators. Each of these approaches has limitations. For example, piezoelectric accelerometers generally have limited low frequency response. Accelerometers based on resonators depend on high quality factor, Q, to achieve the required performance. Piezoresistive accelerometers suffer from temperature sensitivity due to the temperature coefficient of resistivity in silicon. Capacitive sensors are subject to electromagnetic interference.
Many types of micromachined sensors, such as gyroscopes or accelerometers, share one common feature, they use a seismic mass. The underlying principle of operation is that this mass experiences a displacement when subjected to the force being measured. In capacitive sensors, the mass is suspended over a substrate. The variation in the spacing between the mass and the substrate typically produces a proportional variation in capacitance value from which the force can be determined. Different fabrication technologies are employed in an attempt to achieve a sensor with the desired characteristics. These techniques range from bulk and surface micromachining to pseudo-bulk micromachining and wafer bonding.
It is an object of the present invention to provide improvements in surface micromachined sensor devices.
Another object of the invention is to reduce temperature sensitivity of surface micromachined sensor.
And another object of the invention is to provide improved step-up supports for surface micromachined sensor devices.